FIGS. 1 and 2 are schematic diagrams of a water heater structure in the conventional art.
As shown in FIG. 1, a general water heater 1 includes an inflow pipe 10 supplying direct water to a heat exchanger, a heat exchanger 20 that causes the direct water which enters through the inflow pipe 10 to exchange heat with air or water heated by a burner to be hot water, a storage tank 30 temporarily storing the hot water generated by the heat exchanger 20, and an outflow pipe 40 through which the hot water stored in the storage tank 30 flows out.
A direct water temperature sensor 11 measuring the temperature of the direct water that enters through the inflow pipe 10 and a flow sensor 12 measuring the flow of the direct water are installed on the inflow pipe 10.
In addition, a hot water temperature sensor 41 measuring the temperature of the hot water that flows out through the outflow pipe 40 is installed on the outflow pipe 40 to supply hot water having a constant temperature to a user.
Meanwhile, the general water heater 1 may include a bypass pipe 50 connecting the outflow pipe 40 and the inflow pipe 10 to each other to supply water in the outflow pipe 40 to the inflow pipe 10. An internal circulation pump 51 supplying the water in the outflow pipe 40 to the inflow pipe 10 and a check valve 52 for preventing the water in the inflow pipe 10 from being supplied to the outflow pipe 40 without passing through the heat exchanger 20 are installed on the bypass pipe 50.
When the user does not use the hot water for a predetermined time, the temperature of the hot water stored in the storage tank 30 decreases, and as a result, the hot water stored in the storage tank 30 is sent to the heat exchanger 20 again by using the internal circulation pump 51 to be heated.
The temperature of the hot water stored in the storage tank 30 can be constantly maintained by repetitively performing the process.
Meanwhile, as shown in FIG. 2, an external circulation pipe 46 may be connected with the bypass pipe 50. Herein, the external circulation pipe 46 refers to a pipe that is branched off from around a hot water outlet 45 such as a faucet to then be connected with the bypass pipe 50.
In this case, when the hot water is circulated through the external circulation pipe 46 by operating the internal circulation pump 51, the hot water is circulated up to the vicinity of the hot water outlet 45 to preheat the outflow pipe 40, and as a result, the user can use the hot water in a short time.
However, in the water heater 1 in the conventional art, the internal circulation pump 51 is set to operate only before the user uses the hot water.
As described above, since the internal circulation pump 51 is set to operate only before the user uses the hot water, when the user temporarily stops using the hot water and thereafter, uses the hot water again, it takes a while until the hot water starts to be supplied again after supplying of the cold water and this causes inconvenience to users due to a temperature difference of the hot water.
In particular, it is more likely that the temperature difference of the hot water will occur at a hospital, a restaurant, and a health club where the hot water is frequently used and the flow rate of the used hot water frequently varies.